Multifunctional Ligand Passivation <i>via</i> 4-Sulfamoylbenzoic Acid for High-Performance Perovskite Solar Cells

A multifunctional additive, 4-sulfamoylbenzoic acid (SFBA), featuring both amino (–NH2) and sulfonyl (S═O) groups, is introduced into the perovskite precursor solution to simultaneously passivate ionic defects and modulate crystallization. The Lewis basic –NH2 group donates electrons to neutralize positively charged defects, while the S═O moiety exhibits strong coordination with undercoordinated Pb2+ ions. Concurrently, SFBA engages in hydrogen bonding with organic cations (MA+/FA+), retarding crystallization kinetics and promoting the formation of high-quality perovskite films with enhanced crystallinity. Density functional theory calculations confirm strong binding affinities of SFBA toward iodine vacancies, particularly through the sulfonyl group, and differential charge density analysis reveals efficient charge transfer, underscoring a synergistic passivation mechanism enabled by the dual functional groups. As a result, perovskite solar cells incorporating SFBA achieve a champion power conversion efficiency (PCE) of 23.25% with negligible hysteresis, substantially outperforming control devices (22.23%). Moreover, the SFBA-modified devices exhibit markedly improved long-term stability, retaining 90.5% of their initial PCE after 1344 h under ambient conditions (relative humidity 20–35%), compared to only 65.44% for the control devices.